1. Field of the Invention
The present invention relates to an optical sheet for a backlight unit of a thin film transistor-liquid crystal display (hereinafter referred to as a ‘TFT-LCD’) and a TFT-LCD including the same, and more particularly, to an optical sheet that can obtain a sharp optical image by inducing uniform light diffusion while passing light irradiated from a light source lamp disposed on the lateral or rear side of a display therethrough, and a TFT-LCD including the same.
2. Background of the Related Art
A liquid crystal display (LCD) is an ultra-thin image output device with low consumption power, low heat generation and high definition and has recently been spotlighted as image display devices of various industry fields. However, LCD uses liquid crystal made of a non-light emitting material unlike other flat panel display types, and hence requires an additional light-emitting device in order to improve the brightness of a display screen.
The additional light-emitting device includes backlight unit largely classified into a front-light process and a backlight process. The backlight method is an indirect lighting process in which light generated from a light source of a backlight unit attached to the rear side of a display device is guided to reach an opposite side through a light guide plate, and is reflected from a reflection sheet, such as a metal deposition plate or an opaque white sheet and then output to the front side, thus improving the brightness of a display screen. In this backlight process, it is necessary to implement maximum image brightness with minimum consumption power.
Therefore, in order to fulfill this requirement, a method of fabricating an optical sheet in which a light diffusion layer is formed on at least one side of a base sheet so as to transfer light emitted from a light source to a liquid crystal driver has been spotlighted.
Here, the optical sheet plays a role in uniformly diffusing the light, which is irradiated from a light source lamp and then passes through the diffusion sheet or a light guide plate, while having the light pass therethrough without a loss. The optical sheet should have a high total light transmittance and a high haze characteristic as the most important characteristics.
The optical sheet further requires a high optical efficiency, that is, a high luminance characteristic based on these optical characteristics. In other words, distribution and path of light, which is constantly formed from the light source, must be changed to forward light necessary for a LCD.
This optical sheet is typically prepared by coating a composition, comprising polymer resin and spherical particles, on a base sheet, and comprise a body portion to which light is incident and protrusions formed by the particles.
However, the conventional optical sheet has a low aspect ratio between the body portion and the protrusions and accordingly does not accomplish high efficiency necessary for the optical sheet, that is, a desired degree of high luminance.
In view of the above fact, the present inventors had made an effort to improve a low high-luminance characteristic of the conventional optical sheet, and have consequently completed an optical sheet being suitable for a TFT-LCD backlight and having a high total light transmittance and a high haze characteristic in particular, high luminance, including a light diffusion layer in which a diffusion pattern formed of a plurality of protrusions is formed on a base sheet, by specifying a ratio of the radius (l) of a unit body portion of the protrusion formed on the base sheet versus a thickness (d) of an protrusion.